The present invention relates to a mounting structure for mounting a lens in place, and more particularly relates to a mounting structure for an f.theta. lens used as a surface scanning lens of a laser printer or the like.
In an optical system of a laser printer or the like, the required performance with respect to the uniformity of scanning speed and the prevention of the curve of an image surface is ensured by using an f.theta. lens conducting the correction of the tilt caused on a rotational polygonal mirror. This f.theta. lens has an aberration in which an image forming position on a focal surface perpendicular to the optical axis of a lens changes in proportional to an angle .theta. formed between the optical axis of the lens and a beam of incident light. The f.theta. lens is generally supported by a mount through a mounting surface provided on the f.theta. lens.
The conventional lens mounting structure of the type described above is disclosed, for example, in Japanese Unexamined Utility Model Publication No. 63-57610 and Japanese Unexamined Patent Publication No. 3-89311.
In Japanese Unexamined Utility Model Publication No. 63-57610, in order to maintain the level of a lens by preventing the occurrence of burr in the process of molding a mount, a structure is disclosed in which the lens is attached to a mount on which a step portion is provided, the outer circumferential portion of which is formed low. However, in this Japanese Unexamined Utility Model Publication No. 63-57610, the lens is simply positioned on the mount and not fixed thereto. Therefore, this structure suffers from a problem in that when vibration is given to the mount, the lens is likely to be displaced.
According to Japanese Unexamined Patent Publication No. 3-89311, the following structure for mounting an f.theta. lens is disclosed: As illustrated in FIG. 6, a pair of flat reference support surfaces 13 are provided on the mount 12 for positioning the f.theta. lens 11 while the f.theta. lens 11 comes into contact with the pair of flat reference support surfaces 13. Further, an adhering surface 14 is provided between the pair of flat reference support surfaces 13 while the level of the adhering surface 14 is lower than that of the reference support surface 13 by a gap g. The adhering surface 14 and a portion of the flat mounting surface 11A of the f.theta. lens 11 are connected by the adhesive 16. Therefore, a lens distortion is not caused which deteriorates the accuracy of the lens by a difference between the thermal expansion coefficient of the f.theta. lens at the adhering portion and the thermal expansion coefficient of the mount 12. However, in this Japanese Unexamined Patent Publication No. 3-89311, a groove portion 15 for accommodating the adhesive 16 that has overflowed from the adhesive surface side is provided between the reference support surface 13 and the adhering surface 14. Therefore, as the reference support surface 13 and the adhering surface 14 are separated, it is not possible for the reference support surface 13 to prevent the displacement of the lens adhering portion 11B in the direction of the mount (in the direction of arrow A in FIG. 6), the displacement being caused by the shrinkage of the adhesive when the adhesive 16 is hardened and shrunk. For this reason, a distortion is caused in the lens, and predetermined optical characteristics can not be provided.